 /*******************************************************************************
  * Copyright (c) 2000, 2007 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.variables;

 /**
  * A variable with a value that can be set and retrieved. The context in which
  * a value variable is referenced does not effect the value of the variable.
  * A value variable can be contributed by an extension or created programmatically.
  * A contributor may optionally specify an initial value for a variable, or
  * provide a delegate that will initialize the variable with a value.
  * <p>
  * Since 3.3, a variable can be specified as a "read only" preventing users from changing
  * the value after it has been initialized. Furthermore, a read only variable that is
  * contributed by an extension will always load the value from the extension.
  * </p>
  * <p>
  * Example of a value variable contribution with an initial value, the specified
  * variable is created with the initial value "/usr/local/foo".
  * <pre>
  * &lt;extension point="org.eclipse.core.variables.valueVariables"&gt;
  * &lt;variable
  * name="FOO_HOME"
  * initialValue="/usr/local/foo"&gt;
  * &lt;/variable&gt;
  * &lt;/extension&gt;
  * </pre>
  * </p>
  * <p>
  * Example of a value variable contribution with an initializer class, the class
  * "com.example.FooLocator" will be used to initialize the value the first time
  * it's requested.
  * <pre>
  * &lt;extension point="org.eclipse.core.variables.valueVariables"&gt;
  * &lt;variable
  * name="FOO_HOME"
  * initializerClass="com.example.FooLocator"&gt;
  * &lt;/variable&gt;
  * &lt;/extension&gt;
  * </pre>
  * </p>
  * <p>
  * Clients are not intended to implement this interface.
  * </p>
  * @since 3.0
  */
 public interface IValueVariable extends IStringVariable {

     /**
      * Sets the value of this variable to the given value.
      * Since 3.3, this has no effect if this variable is read only.
      *
      * @param value variable value
      */
     public void setValue(String value);
     
     /**
      * Returns the value of this variable, or <code>null</code> if none.
      *
      * @return the value of this variable, or <code>null</code> if none
      */
     public String getValue();
     
     /**
      * Returns whether this variable was contributed by an extension.
      *
      * @return whether this variable was contributed by an extension
      */
     public boolean isContributed();
     
     /**
      * Returns whether this variable is read only.
      *
      * @return whether this variable is read only
      * @since 3.3
      */
     public boolean isReadOnly();
     
     /**
      * Sets the description of this variable to the given value.
      *
      * @param description variable description, possibly <code>null</code>
      */
     public void setDescription(String description);
     
 }

